1. Field of the Invention
The present invention relates to a control device for a pneumatic cylinder using air as its operating medium, and more particularly to a control device for a pneumatic cylinder, capable of controlling the operation speed of the pneumatic cylinder upon reciprocation and braking the reciprocation.
2. Description of the Prior Art
In cases of hydraulic cylinders, an accurate controlling of operation speed and a reliable braking can be easily achieved by operating external valves for adjusting the quantity of supplied oil and shutting off the supplying of oil, the oil as operating medium has a high density characteristic. In cases of pneumatic cylinders, however, it is difficult to achieve an accurate controlling of operation speed and a reliable braking, due to a variation in internal volume of compressed air in the cylinder, which variation is caused by a phenomenon that the compressed air as operating medium varies greatly in density depending on a pressure applied thereto, due to its physical characteristic. In particular, since the speed controlling and braking under low pressure and speed condition are considerably unstable, such pneumatic cylinders are hardly applied to automatic installations and other appliances which require highly precise operations other than a simple reciprocation.
For overcoming the above-mentioned problems encountered in the pneumatic cylinders, there have been proposals of providing a separate auxiliary mechanical device such as a brake lining. However, the provision of such an auxiliary mechanical device causes the whole cylinder construction to be bulk and thus the installation work to be difficult. Furthermore, the cylinder becomes expensive, resulting in a difficulty in practical use.